1. Field of Invention
This invention relates to methods of treating formaldehyde laden wood panels to neutralize free formaldehyde existing in the panels. It has as its intended purpose the reduction in the release of vaporous formaldehyde to the atmosphere within structures, such as mobile homes, where, for example, the panels are typically used for decorative wall panelling. While this represents one field within which the invention is useful, it may also be employed with any form of formaldehyde laden wood product wherein the end use of the wood product results in the significant accumulation of vaporous formaldehyde in an enclosed or semi-enclosed space.
2. Background of the Invention
It is well known in the production of laminated wood panels to use as the laminate glue synthetic resins comprised of the reaction products of formaldehyde with urea, phenol or melamine. It is also common practice to coat panels with one or more coatings based on formaldehyde amino condensates as well as other resins. It has been found and is now well known that vaporous formaldehyde can be released from these panels, some of which is due to unreacted formaldehyde in the glue and coating resins and some of which is due to degradation and/or decomposition products generated over time under acid conditions, elevated temperature and/or humidity. This free, vaporous formaldehyde can be a strong irritant when allowed to accumulate in an enclosed space such as, for example, the interior of a mobile home. It is also suspected of being hazardous to the health of humans when allowed to accumulate to abnormally high levels in the ambient atmosphere. It is, therefore, desirable to neutralize free formaldehyde in the wood products to prevent or substantially reduce its release into the surrounding environment.
One well known technique accomplishing this result is to react the formaldehyde with ammonia to yield hexamethylene tetramine, a less volatile substance than either parent and one that is very stable at normal ambient conditions. The chemical formula for this well known reaction is: ##STR1## In one technique, the formaldehyde containing panel is placed in an enclosed space such as a desiccator saturated with gaseous ammonia from an aqueous ammonia solution. The vaporous ammonia released in the desiccator migrates into the porous wood panel to react with and neutralize the free formaldehyde in a very effective manner. Comparative tests between untreated control samples and treated samples have shown that vaporous formaldehyde concentration in the atmosphere can be reduced by an order of magnitude. For example, one such laboratory test showed a reduction from 8.2 parts per million (ppm) to 0.5 ppm. Unfortunately, however, while exposing panels to vaporous ammonia for this purpose is very effective, the technique does not lend itself well to high volume wood panel production and processing at normal production rates. The technique would require considerable investment in an enclosed facility to maintain the panels exposed to vaporous ammonia. Also, the strong ammonia odor involved, as well as environmental pollution considerations could make the technique unwieldly and impractical for plant use without extensive and costly equipment addition and/or modification.
An alternative technique involves coating the wood panels with an aqueous ammonia solution. Although this technique facilitates the application of ammonia to the wood product, it is less effective than long term exposure to vaporous ammonia in neutralizing the formaldehyde. It has been found that the ammonia coating is effective mainly only as a surface treatment since the ammonia is quickly released to the ambient atmosphere and does not effectively penetrate the panel to reach the entrained free formaldehyde. When used in open plant processing areas, there is considerable worker exposure to vaporous ammonia with consequent unpleasant odor and irritation, as well as environmental control problems.
It is, therefore, an object of the present invention to provide a method for treatment of formaldehyde laden wood products that is effective in the reduction of free formaldehyde in the product while at the same time avoiding the disadvantages of prior known techniques.
It is also an object of the invention to provide a method of treating formaldehyde laden wood products that is particularly well adapted to the high volume treatment and handling of flat line wood panels.
It is a further object of the invention to provide a formaldehyde treatment method which is readily adaptable to high volume manufacturing plant processing without undue worker exposure to vaporous ammonia.
It is yet another object of the invention to provide a formaldehyde treatment method which can be employed with existing plant equipment and which does not require investment in extensive off-line treatment and handling facilities, or additional pollution control equipment.